A consistent problem encountered in seismic data interpretation is that of "multiples". When acoustic seismic energy is generated, it travels though the earth subsurface until it encounters an interface created by a density and/or velocity change in subsurface formations. The interface will reflect a portion of the acoustic seismic energy, refract another portion and permit a portion to pass through the interface. Seismic energy which has been reflected more than once from the interface is termed a "multiple". It is desirable to attenuate these reflections so that the primary reflected acoustic energy is evident from which an approximation of the subsurface formations can be implied. Normally, this data is collected in common depth point (CDP) gathers and processed to develop an approximation of the subsurface formations in a given area.
A conventional way to process CDP data, as illustrated in FIG. 1, is to collect the data at block 12, apply a spike deconvolution operator at block 14, determine the primary stack velocity at block 16, correct normal moveout (NMO) with the primary stack velocity at block 18, stack the common depth point data at block 20 and display it as display "A" at block 22. A possible addition is to apply a gap deconvolution operator at block 24 to the stacked data before displaying the stacked section at block 26.
This conventional method for processing CDP data provides satisfactory results in most cases but has problems when significant long period multiples are present with either a short offset distance or approximately equivalent travel velocities in adjacent formations. When these conditions occur, a process using F-K domain filtering of data prior to stack is used, as illustrated in FIG. 2. Common Depth Point data is received at block 40 and is normal moveout corrected with multiple velocity at block 42 after the multiple stack velocity is determined at block 44. The multiples are filtered in the F-K domain at block 46 and multiple velocity normal moveout is removed at block 48. A spike deconvolution operator is applied at block 50 and the normal moveout is corrected with the primary stack velocity at block 52, the primary stack velocity having been determined at block 53. The common depth point gather is stacked at block 54 and displayed as display "C" at block 56 of FIG. 2. However, this procedure is expensive and may quadruple the cost of processing data.